Drag stabilized low viscosity melt spinning process

ABSTRACT

AN IMPROVED STABILIZATION PROCESS FOR FORMING FILAMENTS FROM STREAMING LOW VISCOSITY MELT MATERIALS BY SIMULTANEOUSLY PREVENTING DISRUPTIONS IN THE FRAGILE, INCOMPLETELY SOLIDIFIED PORTION OF THE STREAM DIE TO THE DRAG INTERACTION BETWEEN THE STABILIZER STREAM AND SURROUNDING GASEOUS ATMOSPHERE AND UTILIZING THE DRAG TO FORM A HELICAL-LIKE CONFIGURATION IN THE SOLIDIFIED PORTION OF THE STREAM WHICH PERMITS APPLYING SUFFICIENT TENSION THERETO TO ENABLE FILAMENT TAKE-UP.   D R A W I N G

Feb. 6, 19.73 w. J. nmvb'r'r. 4a.. ET AL.

3,715,419 DRAG STABILIZEDLOW VISCOSITY MELT'SPINNING PROCESS Filed Oct.27, 1969 3 Shuts-Shunt 1 lllllllil 1 Angle of F ilumem with VerficalvFIG. I

Spinning Velocity (V FIG.

v V. l j C n m v o o o mwwm w w o w w a O 25 m m xiv W 2 2 :l 1 i u V b8 .4 O A 3 A B d 4 Q J 9, degrees OBERT E. CUNNINGHAM FIG 3 ATTORNEY/Q)I Feb. 6, 1973 w,' PR|VQTT,' JR ET AL 3,715,419

DRAG STABILIZED LOW VISCOSITY MELT SPINNING PROCESS Filed Oct. 27. 1969s Sneets-Sheet 2 32 3O REACTANT/COOLANT l GAS i a E 38 SUPPORT GASFIG.4. ZONE B SUPPORT H GAS INVENTORS WILBUR J. PRIVOTT, JR.

B OBET E. CUNNINGHAM TAKE-UP N ATTORNEY Feb. 6, 1973- I w, pRwoTT, JR"ET AL I 3,715,419

DRAG STABILIZED LOW VISCOSITY MELT SPINNING PROCESS Filed Oct. 27, 1969'3 Sheets-Sheet a I 3L m b l 0: LL! E9 Ll.

D0 Dq Db 2 FREE FALL DISTANCE Q 3 J h l 5 FREE FALL DISTANCE CL FIG. 5.

TO COLLECTION 7 TO SPINNING PLATE HEAD l" FIG. 6.

DCAMPLIFIER INVENTORS I WILBUR J,PRIVOTT, JR.

RECORDERE BY OBER E. CUNNINGH M ATTOR N United States Patent M 3,715,419DRAG STABILIZED LOW VISCOSITY MELT SPINNING PROCESS Wilbur J. Privott,Jr., and Robert E. Cunningham,

Raleigh, N.C., assignors to Monsanto Company, St. Louis, Mo.Continuation-impart of application Ser. No. 680,898,

Nov. 6, 1967. This application Oct. 27, 1969, Ser.

Int. Cl. B28b 3/20; B22d 11/00 U.S. Cl. 264-82 7 Claims ABSTRACT OF THEDISCLOSURE CROSS-REFERENCES TO RELATED APPLICATIONS This application isa continuation-in-part of the copending and commonly assignedapplication Ser. No. 680,- 898, filed on Nov. 6, 1967, and nowabandoned. Related copending and commonly assigned applications are Ser.No. 829,216, filed June 2, 1969; Ser. No. 863,311, filed Oct. 2, 1969;and Ser. No. 863,707, filed Oct. 3, 1969.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates generally to the formation of filaments and fibers directly fromlow viscosity melt materials and, more particularly, to a process ofdecelerating and supporting a molten stream extruded from a lowviscosity melt.

Description of the prior art In attempting to form filaments or fibersdirectly from a streaming melt material of low viscosity, the initialproblem is to stabilize the liquidous portion of the stream, pending itssolidfication, against an intrinsic tendency to break-up into shot dueto surface tension. The U.S. Pat. 3,216,076, issued to Alber et a1. andthe above reference application Ser. No. 829,216 incorporated by way ofrefference herein disclose unique and practical approaches to solvingthe problem. In quite general terms, the approaches involve the conceptof film-stabilized melt spinning wherein a low viscosity melt materialis freestreamed under carefully controlled conditions through selectedatmospheres which react or decompose upon exposure to the stream andform a film about the periphery thereof. The film serves to stabilizethe stream against surface tension-induced breakup pendingsolidification by normal heat transfer phenomena.

The term low viscosity is used in this application to define viscositiesof 10 poises or less. The materials generally employed to form filamentsand fibers in accordance with low viscosity melt spinning techniques arethose materials which are normally solid at 25 C. Among materials whichhave these characteristics are the metals, alloys thereof, intermetalliccompounds, ceramics, metalloids, and various salts.

Examples of the metals which may be spun are beryllium, cobalt,aluminum, thorium, nickel, iron, copper, gold, uranium, zinc, manganese,magnesium, tin, and al- 3,715,419 Patented Feb. 6, 1973 loys of suchmetals. Representative of the low viscosity ceramics are alumina,calcia, magnesia, zirconia, and mixtures of these and other oxideswherein the mixtures exhibit the above discussed characteristics.Metalloids, such as boron and silicon, salts such as potassium chlorideand a variety of other normally solid inorganc materials with low meltviscosities are capable of being spun into filaments and fibers.

Subsequent to the advent of the low viscosity melt spinning techniques,the need to solve other related problems was soon recognized. Forexample, in addition to the inability of a low viscosity melt stream towithstand surface tension-induced disruptions while in the liquid state,it has also been noted that such a stream is susceptible to forcesengendered by the impact or deceleration incident to taking up thestreaming body after solidification. The forces generated during suchdeceleration often result in shearing rupture or deformation of thestream.

It was disclosed and claimed in the aformentioned application Ser. No.863,311, filed Oct. 2, 1969 that there is a point (D,,), as measuredfrom the stream origin, above which any given deceleration of the streamresults in repeated disruptions; a point (D as measured from the streamorigin, above which the stream must be decelerated if repeated tensilebreaking is to be avoided and that the decelerating of the streamintermediate the points (D,,) and (D affords the obtaining of continuousfilaments by obviating the stream disruptions and tensile breaks.

Still another problem was disclosed in application Ser. No. 863,707incorporated by way of reference herein. Briefly, it was found that whenthe solidified portion of the stream deviated from its vertical path,the drag forces induced by the surrounding atmosphere caused thedeviations to increase in amplitude and propagate up the stream into theliquidous portion. The drag-sustained deviations cause disruptions inthe stream continuity.

Application Ser. No. 863,707 however, also discloses and claims amethod, the practice of which advantageously avoids the effects of thedeviations by maintaining the upstream velocity of the drag-sustaineddeviations less than the velocity of the stream so that the undesireddeviations are caused to move harmlessly away from the fragile liquidportion of the stream.

In the continuous take-up of the solidified stream or filament, it maybe necessary to apply tension (albeit slight) to the stream after it hassolidified. The portion of the stream which has the least tenacity isthe liquidportion at or near the extrusion orifice. When, however, thetension needed for wind-up is applied to the solidified portion of thestream, it is transferred to the liquid portion, causing the stream tobe disrupted in the manner identical to that experienced when thestream, extends to a point (D at which it breaks under its own weight.

Unexpectedly, however, it has been found that the effect ofdrag-sustained deviations may be advantageously employed to facilitatefilament take-up while avoiding stream breaks or disruptions due to bothtension and drag-sustained deviations. Generally, proper take-upconditions may be maintained in accordance with the present invention asfollows: (1) controlling the conditions in a first zone which extendsbelow the liquidous portion of the stream so as to cause the velocity ofthe drag-sustained deviations up the stream to be less than the velocityof the stream; and (2) controlling the conditions in a second zoneimmediately below the first zone so as to cause the velocity of thedrag-sustained deviations up the stream to be greater than the velocityof the stream. As a consequence, the stream in the second region attainsa helical-like configuration which cannot pass into the first region dueto the conditions imposed therein. The presence of the helicalconfiguration in the solidified portion of the stream, however, allowstension to be applied to that stream zone without transferring thetension to the fragile hquidous portion of the stream.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects,features, and advantages of the present invention will become apparentfrom the following, more detailed description and the accompanyingdrawings in which:

FIG. 1 graphically depicts the variation in vertical force (F,,) actingupon a stream as a function of the angle of stream deviation from thevertical;

FIG. 2 is a typical plot of the variation in the propagation velocity (Vof drag-sustained stream deviations as a function of the stream orspinning velocity (V propagation velocity being normalized relative tospinning velocity;

FIG. 3 is a typical plot of the variation in vertical force (F upon astream with stream deviation angle for a series of stream velocities (VFIG. 4 is a simplified vertical, partially sectionalized view of aspinning apparatus which may be employed in the practice of the subjectprocess;

FIG. 5 graphically depicts the interrelationship of fiber length (L)with stream free-fall distance for the case where the point of impactbreakage deceleration (D,,) is maintained upstream of the point oftensile breakage deceleration (D the condition which must obtain forindefinite length production; and

FIG. 6 is a schematic circuit diagram of conventional make-up which maybe employed to electrically monitor and record stream continuity whereissued from electrically conductive melts.

DESCRIPTION The aforementioned application Ser. No. 829,216 discusses indetail the theory of low viscosity melt spinning and fundamentalconditions necessary for proper stabilization of the molten streampending solidification. For purposes of this disclosure, it is necessaryto state only that the molten stream must be extruded at velocities anddiameters which satisfy a range of values which are calculated from adimensionless quantity known as the Rayleigh parameter (Ra). TheRayleigh parameter is defined as where V is the extrusion velocity,cm./sec.

p is the melt density, gm's./cm.

D is the stream diameter, cm.

7 is the stream surface tension, dynes/cm.

The range of values for the Rayleigh number is l to 50. For optimumspinning conditions, it is preferred that a value for the Rayleighparameter be between 2 and 25. Thus, for example, given a melt densityof 4 gms./cm. a surface tension of 1000 dynes/cm., and a stream diameterof 0.03 cm., it is necessary to have an extrusion velocity between 90 to4500 cm./sec. to be within a Rayleigh parameter range of 1 to 50.

Although application Ser. No. 863,707 is incorporated herein byreference, it is thought that the following discussion on drag-sustaineddeviation will be helpful in more clearly pointing out the presentinvention. Initially, it will be observed that any deceleration of thestream must result in a deviation from its original vertically straightpath. As distinguished from the general configuration that ischaracteristic of stream deviations within the liquid region,drag-sustained deviations are initiated in the relatively highermodulus, solid downstream region. The increased rigidity of the streamresults in the formation of a threet imensio h lical-li e (as PPQ1 t9sinuou onfiguration which if allowed to will grow and move unimpeded.

Starting from literature studies of the viscous drag forces acting uponstreaming bodies (see for example, Sakiadis, B. C., AIChEJ. 7, 467(1961) and Knudsen, J. G. and D. L. Katz, Fluid Dynamics and HeatTransfer, McGraw-Hill, New York, 1958), a reasonably close approximationof the total downward force acting upon a streaming body has beenderiven as given by:

F unit length=the force acting upon the stream/unit length, dynes/cm.

r=stream radius, cms.

g=gravitational acceleration, 980 cm./sec.

p =Stf6aITl density, gm./cm.

,u=spin gas viscosity, poise V =stream velocity, cm./sec.

V =velocity of the gas into which the stream is extruded,

cm./ sec.

=spin gas density, gm./cm.

0=angle of stream deviation between axis of the stream and the verticaldegrees.

As may readily be appreciated, it is impossible, at least within therealm of practicality, to constrain a freely streaming body to move in aprecisely straight path. Even though one takes elaborate precautions, itis virtually impossible to isolate the stream from at least initiallyminor disturbances engendered, for example, by controlled, though minor,fluctuations in extrusion conditions, eddy currents and the like due tosuch as minor orifice imperfections and external vibrations.

As shown by Equation 1 above, the total downward force per unit lengthon the stream varies with the angle of deviation of the stream from thevertical. FIG. 1 depicts a curve for a solution of Equation 1 as afunction of the angle of stream deviation from the vertical. As thereindicated, any deviation of the stream from the vertical less than 0leaves the entire length of the stream in a positively tensioned state,with the result that there is no tendency for the stream to undergofurther deviation or bending. That is, because a net tensional ordownward force remains upon the stream at deviations of a magnitude lessthan the angle of 0 the stream tends to return to its originalvertically straight path even though initially deviated by some streamdisturbing force. Once some portion of the filament, by whatever event,achieves an angle greater than 0 from the vertical, this portion will bedecelerated in that the interaction between gravity and the increaseddrag force acting upon such deviated portion results in the impositionof a net upward, or compressive force upon the stream. Further, theforce of oncoming upstream portions will tend to increase the angle ofthis portion of the stream and the filament will be urged to move to anangle 0 with the vertical. As shown by the typical curve of FIG. 1, theonly two stable equilibrium confiurations of the stream supplied at arate V are a substantially straight, vertically falling stream with aconstant speed V or a stream falling at an angle of deviation 0 with thevertical at a velocity of V cos 0 Any other magnitude of deviation willbe found unstable, with the stream returning to either the configurationaccompanying an angle of deviation of 0 or a substantially verticallystraight path. Thus, it is seen that, for a given net tensional forceacting upon a stream passing in a state of equilibrium along a straight,substantially vertically downward path, there exists an angle ofdeviation 0 hereafter termed the angle of threshold deviation, belowwhich the stream is, under the influence of gravity or other streamaccelerating or tensioning forces, returned to the equilibrium state ofits original, straight-line path, and above which a net upward, ornegative (compressive) force comes t9 act upon the tlt viated portionurging it to an angle of deviation hereafter termed the angle ofequilibrium deviation. Further, as the net tensional force acting upon avertical, undeviated portion of the stream decreases with, for example,an increase in the force of viscous drag acting thereon, the angle ofthreshold deviation 0 decreases. Thus, the magnitude of streamdisturbance necessary to initially deviate the stream to 0 decreaseswith decreasing stream tension.

In the case where a stream portion has come to occupy the angle ofequilibrium deviation 6: it is clear that oncoming upstream portionsmust be decelerated from a velocity V to a velocity l cos 0 assuccessive portions undergo deviation or helical bending to the angle ofequilibrium configuration 0 The effect of this successive bending of thestream is the propagation of the helically configured deviation alongthe stream. It is this understanding of the mechanism of drag-sustainedstream deviations that has led to the discovery that, by manipulation ofthose spinning conditions affecting the magnitude of the viscous dragforce, one can control the formation and streamwise propagation velocityof such deviations.

It has now been experimentally confirmed that a reasonable approximationof the propagation velocity, relative to the stream, of a drag-sustainedstream bending or deviation is given by the relationship:

wherein The magnitude and direction of such velocity of propagationrelative to the orifice (V is obtained simply by subtracting the streamvelocity from the value given bv Equation 2. Thus,

wherein V ==the normalized velocity of the velocity of propagationrelative to the orifice and being negative in value when propagatingtoward the orifice, cm./ sec.

V the velocity of propagation of the stream deviation relative to thestream as given by Equation 2, cm./sec.

V =the velocity of the stream, cm./ sec.

There is depicted in FIG. 2 a typical plot of the propagation velocityor drag-sustained deviations as a function of the stream or spinninngvelocity wherein the propagation velocity is normalized relative to theorifice. For example, where the velocity of propagation matches spinningvelocity, the deviation progagates at a velocity relative to the orificeor normalized velocity, of zero and the deviation would remain a fixeddistance from the orifice. A plot is shown for the cases ofcounter-current, stagnant and co-current spin gas fiow. As indicated,for spinning velocities greater than the critical value V anydisturbance which causes a stream deviation to an angle greater than 6would propagate upstream to the fragile liquid region to result ineither total breakup of the stream or a jointed appearance in theresulting filament. For steam velocities less than the critical spinningvelocity V any stream deviation would be swept harmlessly downstream.

It should here be noted that the representation in FIG. 2 is madeassuming the stream is of constant modulus along the length underconsideration. In reality, the effective stream modulus may be found todecrease with increasing stream temperature encountered at progressivepoints upstream so that, where conditions are such that the disturbancepropagates at a velocity sufficient to move upstream relative to theorifice, the length over which such stream bending acts becomes less andless until a point is reached where the propagation becomes arrested bya sharp bend, resulting in either broken lengths or filaments exhibitingknee-like joints.

To gain a better understanding of the interrelationship of the verticalforce system acting upon a filamentary stream and the velocity at whichstream deviations are caused to propagate, reference is now made to theshowing of FIG. 3 where, employing Equation 1, the variation in verticalforce per unit length with angle of stream deviation for a range ofspinning velocities is shown. Forces acting in the down stream directionare positive. The FIG. 3 showing is for the case of an 86 microndiameter, 62 wt. percent lead/38 Wt. percent tin stream passing througha stagnant atmosphere of 93 volume percent helium and 7 volume percentoxygen. With the fiber radius, density and modulus, and the gasviscosity, density and velocity thus established, the data necessary tocalculate the vertical force at varying spin velocities and angles ofstream deviation is provided.

As shown in FIG. 3, at a zero spin velocity (V the vertical force perunit length acting upon the stream equals the stream weight. Up to aspinning velocity of about 625 cm./sec., the net force acting upon thefiber is always in the downward, or positive direction, regardless ofthe angle of the filament with the vertical, with the result that anyincipient stream deviation is immediately overcome and the streamreturned to its original path. Consequently, no drag-sustainedpropagation is possible. As the spinning velocity is increased, a pointis reached at which, once the stream suffers a deviation greater than 0the resultant drag-sustained propagation due to the net upward, ornegative, force acting upon the stream exactly equals the spinning rate,with the result that the deformation is stationary relative to theorifice as it rides the stream in treadmill fashion. According toEquation 2, a spinning velocity of approximately 2,050 cm./sec. isrequired to satisfy this condition. As previously discussed, it has beendiscovered that, under the conditions above specified, this constitutesthe maximum allowable spinning velocity or critical spinning velocity Vif non-jointed, continuous lengths are to be obtained. At higherspinning velocities, an upstream force is imposed upon the stream ofsuch magnitude as to cause any stream deviation initially exceeding 0 topropagate at a velocity greater than the spinning velocity to moveupstream relative to the orifice to a point where stream strength hasdecreased sufficiently to arrest such propagation by permanentdistortion or breakage. At lower spinning velocities, any 6 deviation ofthe stream will, due to the reduced upward force, propagate at avelocity less than the spinning velocity to thereby pass harmlesslydownstream. It is to be recognized that, in general, a precise balancebetween propagation and spinning velocities is not likely of observationsince very minor variations in spinning conditions, particularly asregards spinning velocity or gas conditions, would result in movement ofthe deformation either upstream to a point of ultimate disruption orharmlessly downstream.

As will be understood, as the upstream-acting drag force increases with,for example, increasing spinning velocity, the threshold or minimuminitial stream deviation 0 beyond which the drag force is suflicient tofurther deviate the stream to the stable 0 position decreases. So longas a stream is conveyed with such precision as to avoid any initialdeviation greater than 0 drag-sustained deviations and their propagationwill not be sustained.

It has been observed, however, that particularly in the case of lowdensity melts and/or small diameter streams, deviations greater than arevirtually impossible to avoid. Also, where it is found necessary toresort to countercurrent gas flows in order to avoid stream breakage dueto gravity (as may be the case with relatively large diameter streams ofhigh density), the extent to which gravity, or stream weight, may becounteracted by, for example, a drag force is limited out of the sameconsiderations. It will often be found desirable to impose drag forcesof such magnitude as to result in a value for 6 so small that it will befound most difficult to isolate the stream from incidental 0 deviations.Again, once such a magnitude of initial deviation occurs, it is criticalthat the propagation of the resultant drag-sustained deviation becontrolled not to exceed the spinning velocity if permanent distortionsof the weak upstream region are to be avoided.

As determined by calculation from Equation 2, a still further increasein the spinning velocity above the critical spinning velocity of 2,050cm./sec. (V results in a propagation velocity of drag-sustaineddeviations greater than the spinning velocity, with the result that adeviation moves upstream to a point of ultimate stream disruption. Forexample, at a velocity of about 2,170 cm./sec., the gravitational andviscous drag forces are of equal magnitude at an angle of zero deviationand the net force of drag versus gravity acts upstream at any otherangle. Under these conditions, even the most minor stream deviation isdrag-sustained and propagated at a very rapid, theoretically infinite,rate.

It may readily be appreciated that, for other stream and gascompositions and other spinning conditions, a force diagram such asdepicted in FIG. 3 may reflect considerably different values, but willgenerally conform to the pattern there indicated.

Among the spinning parameters which may readily be varied to accomplishthe desired interrelationship between the propagation velocity of streamdeviations and spinning velocity are those of stream radius, modulus anddensity and spin gas density, viscosity and velocity. In general, thecritical spinning velocity (V (i.e., that velocity above which, under agiven set of conditions, propagational velocity is found to exceedstream velocity with concomitant migration of the deviation relative tothe stream source) increases with increasing stream radius. Accordingly,with the increasing tensional force of larger and larger streams due tothe influence of gravity, the greater the permissible drag force belowwhich upstream migration is forstalled. Similarly, the critical spinningvelocity increases with increasing melt density. Accordingly, in thecase of very low density melts, it will normally be found necessary toresort to co-current spin gas flow or other modes of reducing streamdecelerating force and/or increasing stream tension within those regionswhere migration of drag deviations is to be avoided. Contrary to whatmight be expected, it has been found that a fairly wide variation instream modulus has little effect upon the critical velocity (V Spin gasdensity has been found to have a significant effect upon the criticalspinning velocity, assuming that gas viscosity remains constant. Thisassumption is warranted for many of the gases, but not for all. Forexample, helium and oxygen have approximately the same viscosity, but ithas been found that spinning into a primarily helium atmosphere can beexecuted without upstream migration at much higher velocities than intoan atmosphere having the density of oxygen. Similarly, the effect of gasviscosity is also quite pronounced, especially in the cases of lowerdensity streams and/or smaller diam eter streams.

Spin gas velocity is another readily controlled spinning parameterhaving a significant effect upon the propagational velocity ofdrag-induced stream deviations and is found particularly convenient inthat it may be controlled independently of the factors of stream sizeand composition, as well as spin gas composition. Obviously, the higherthe co-current gas velocity, or the lower the countercurrent velocity,as the case may be, the less the viscous drag force and the greater thecritical spinning velocity.

Aided by the foregoing observations regarding the propagation of streamdeviations, it has now been discovered that, by imposing a particulardifferential or segmentation of the system of forces imposed alongadjacent stream regions, such deviations may be localized to effect astabilized elastic deformation of the stream within a selected regiontherealong to thereby decelerate and support same against tensilebreakage while isolating the fragile upstream region from thedisturbances attending such deceleration and accumulation. In furtherdetailing this practice, reference is now made to FIG. 4 as symbolicallydepicting the basic interrelationship. Within the upstream region of thespinning column labeled Zone A, the tensional or accelerating andbending or decelerating forces acting upon the stream are controlled tomaintain the velocity of propagation (V of stream deviations less thanthe stream or spinning velocity (V This is to say that the force systemimposed upon the stream within Zone A is such that, if the angle ofthreshold stream deviation 0 is exceeded and the stream thus furtherdeviated to the angle of equilibrium configuration 0 (wherein the up anddownstream forces are in equilibrium), the propagation of thisconfiguration along the stream would proceed at a rate less than thestream velocity. Thus, as previously explained, the deviation could notmigrate upstream relative to the orifice, but would be passeddownstream. In normal operation, it will be found preferable to maintaina force system within the upstream region of Zone A such that the streamremains under a net tensional force for any given angle of deviation,with the result that no propagation can occur and the deviation decaysto allow the stream to return to its original path. Such a condition isgraphically represented in FIG. 3 by that family of curves lying aboveor on the tensional side of the zero force line, which is to indicatethat no amount of initial stream deflection will result in theimposition of that net upstream or bending force necessary to furtherdeform the stream to the equilibrium configuration angle 0 much less tocause such configuration to propagate at a velocity greater than that ofthe stream.

Within the downstream region labeled Zone B in FIG. 4, the system oftension or accelerating and bending or decelerating forces is controlledto maintain the velocity of propagation of stream deviations, onceinduced, greater than stream velocity to thereby cause an upstreammigration of such deviations to the locus of demarcation between thestream and downstream regions. As previously set forth, when the forcesystem imposed along the upstream region is so maintained taht thebending rate is less than the stream or extrusion velocity (V anydeviation propagated with Zone B is prevented from passing into Zone A,and migrates only to the upstream extent of Zone B to occupy a stableposition relative to the stream origin. Thus, below the fragile regionwith Zone A, the stream is smoothly decelerated and elasticallycontorted at a localized point to form an accumulation which serves tocushion the upper region against the disturbances attending collection.

The force system maintained along the downstream region of Zone B may besuch that the angle of threshold deviation 6 is very small oressentially zero, in which case even a very small initial deflection ofthe stream results in a rapid upstream migration relative to theorifice. For example, under the conditions specified for the graphicalportrayal of FIG. 3, it is seen that the gravitational and drag forcesare of equal magnitude at an angle of zero stream deviation for aspining velocity of approximately 2, cm./sec. and the net of drag vs.gravity acts upstream at any other angle. Thus, even the most minorstream deviation would be drag-sustained and rapid- 1y propagatedupstream to the juncture with Zone A. Accordingly, where the forcesystem imposed along Zone B is, concomitant with a close balance betweenstream accelerating and deceleration forces, characterized by an angleof threshold deviation verging on zero, it is found that the stream isimmediately deviated to the angle of equilibrium configuration 0 onpassing into Zone B. This, of course, is due to the fact that, as anecessary incident to the disturbances attending normal spinningoperations, the stream is constantly undergoing deflections which,though minute, are sufficient to exceed the small angle of thresholddeviation 0, accompanying a close balance between stream acceleratingand decelerating forces.

Where the force system imposed along Zone B is characterized by an angleof threshold deviation 0 too large to be reliably exceeded by incidentalstream deflections, the stream must be purposely deflected through anangle greater than 0 This is symbolically denoted in FIG. 4 by the useof a deflection plate located at the demarcation between Zones A and B,but the initial deflection of the stream beyond the angle of thresholddeviation may be accomplished by a variety of techniques. For example, alateral jet of gas or -magnetic field may also be employed to initiallydeflect the stream.

The differentiation or segmentation of the force systems acting alongZones A and B necessary to attain stabilization of stream deviations isreadily accomplished by any one or more of a variety of manipulations.No matter how such a differentiation in force systems is effected, it isalways characterized by a decrease in stream tension and/or an increasein stream bending or decelerating forces in passing from Zone A to ZoneB, the diiferentiation being suflicient to increase the bending ratefrom a value less than stream velocity in Zone A to one greater thanstream velocity in Zone B. For example, the stream may be subjected toan increased viscous drag force on entering Zone B by virtue of passingthrough a supporting gas having a greater density and/or viscosity tothat of Zone A. Similarly, the gas within Zone B may be maintained at alower co-current or higher counter-current velocity, as the case may be,than that of Zone A. For example, extremely heavy or dense filaments mayrequire a countercurrent flow of supporting gas in Zone A to preventtensile breaking from occurring in the molten portion of the stream. Toprovide the helical-like configuration in Zone B, it is necessary toincrease the velocity of the countercurrent flow in Zone B. As shouldnow be apparent, the converse may be true for light filaments. Asindicated in FIG. 4, the latter may be accomplished by introducing acounter-current flow of support gas within the lower region of Zone B. Adecrease in counter-current gas flow on passing from Zone B to Zone A isreadily accomplished by, for example, utilizing an enlarged spin chambercrosssection within Zone A to effect a reduction in countercurrent flowon entering the larger zone with a consequent decrease in the force ofviscous drag upon the streaming body. Numerous combinations of thesetechniques of force system diflerentiation between Zones A and B may beemployed. Also, though it may not be feasible to segment those streamcharacteristics affecting the system of forces acting thereupon, such asspinning velocity, stream density and radius, it should now berecognized that, where a given differential in the force systems ofZones A and B is found insufficient to sustain a velocity of propagationwithin Zone B greater than the stream velocity, the spinning or streamvelocity may be increased to a level where such a condition obtainswithin Zone B, subject of course, to the limitations on stream velocityimposed out of considerations attending stabilization of the liquidregion and avoiding the generation of a drag force within Zone Asuflicient to render deviation propagation greater than the stream orextrusion velocity. In other words, for a given dilferential in forcesystems, there exists a range of stream velocity wherein the velocity ofpropagation may be maintained less than the stream velocity 10 withinZone A and greater than the stream velocity Within Zone B. If spinningwithin the prescribed spinning velocity range is found inexpedient, thedifferential in force systems is readily modified, as before indicated,to accommodate a more workable spinning velocity.

Though the foregoing discussion has largely been in terms of adifferential in spin gas conditions between the upstream and downstreamregions, it is to be recognized that the required segmentation of forcesystems may also be accomplished by establishing a differential instream momentum between the two regions to thereby allow a differentialstream bending rate or velocity of propagation even in the presence ofidentical gas conditions within the two regions. Segmentation of streammomentum between the two regions is readily established by imposing achange in the stream configuration and a consequent change in the forcesystem acting therealong as between the two regions to result in achange in momentum such as to reduce the resistance to stream bendingwithin the downstream region. The desired change in stream momentumconcomitant with a change in configuration may be effected by imposing asustained deviation of the stream with Zone B by an externally appliedforce. Such a deviation may be accomplished, for example, by adeflection plate, such as is symbolically indicated in FIG. 4. Eventhough conditions may be such that the propagation velocity of adeviation in a stream from the vertical to an equilibrium configuration0 is less than the spinning velocity, the imposition of a sustaineddeflection, with the accompanying change in momentum, results in a forcesystem along the continuously deflected portion of the stream such thatthe propagation velocity of a further deviation superimposed thereuponis greater there than along an undeviated portion. Thus, by propercontrol of the magnitude of the sustained stream deflection, thevelocity of propagation (V within Zone B can be caused to exceed thespinning velocity (V to thereby form a stabilized helical deviationbelow Zone A under all conditions for which there exists a net upwardforce on the stream falling on some angle. Said differently, if thereexists an angle of threshold deviation 0 and an angle of equilibriumconfiguration 0 for a given set of conditions, a stable deviation can bemaintained by providing a sustained deviation of the stream below Zone Aof sufficient magnitude that the propagation velocity of a furtherdeviation beyond 0 exceeds spinning velocity. Again, this mode ofoperation can be used, but is not limited to situations where the gasconditions in the upstream and downstream zones are identical.

A further important aspect in the practice of the present inventionrelates particularly to the drag-sustained production of indefinite orcontinuous length articles extruded from low viscosity melts. Thispractice is generally characterized by control of the locus ofdemarcation between the diiferential in force systems imposed along theupstream and downstream portions (Zones A and B, respectively) relativeto a particular interrelationship of the breaking characteristics of agiven stream. As stated previously, application Ser. No. 863,311describes and claims a process by which continuous filaments may beobtained. Because the teachings therein are highly relevant to thepresent invention, it is necessary to briefly discuss the breakingcharacteristics of a stream although for a more detailed explanationreference should be made to application Ser. No. 863,311 which isincorporated by way of reference herein. Low melt viscosity streams arecharacterized by a point (D as measured from the stream origin andhereinafter termed the point of impact breakage deceleration, abovewhich the application of a given deceleration results in repeated impactdisruption of the stream. Further, there exists a point (D hereinaftertermed the point of tensile breakage deceleration, above which thestream must be decelerated if repeated tensile breaking is to beavoided. Thus, where stream continuity is to be preserved in the serviceof producing articles of indefinite length, the present invention isembodied by the manipulative sequence of intercontrolling the forcesystem imposed upon the stream relative to stream state to maintain thetensile breakage deceleration point (D downstream of the impact breakagedeceleration point (D and maintaining the locus of demarcation betweenthe differential in force systems imposed along the upstream anddownstream portions at a position intermediate the points D and D Thecontrol of the force system acting upon low viscosity streams such thatthe point D is maintained upstream of the point D may be effected by anyone or more of a variety of modes, as typified in the application Ser.No. 863,311. The proper interrelationship of the impact and tensilebreakage points, D and D is diagrammatically indicated by the graphappearing in the upper portion of FIG. wherein the free-fall distance ofthe stream is plotted against fiber length.

In the present discussion, the term free-fall distance shall be taken todenote that vertical distance between the stream origin or orifice andthe point at which the stream undergoes initial deceleration. Forexample, in FIG. 4 the position of the deflection plate or collectionsurface constitutes the point of initial stream deceleration. However,it is to be emphasized that free-fall distance is not necessarilydefined by a position of a solid collection surface such as depicted inFIG. 4. Such a surface is merely to be taken as symbolic of that pointbelow the orifice at which a decelerating force is imposed upon thestream. Though this force may arise by the sudden impact of the streamupon a solid surface, a more gradual stream deceleration, such as may beeffected by causing the stream to pass through a denser and/orcounterfiowing spin atmosphere may as well give rise to this force.Similarly, a more gradual stream deceleration may be achieved by theimposition of a suitable electrostatic field. It is only for the purposeof simplicity that the following discussion is made largely in terms ofeffecting initial stream deceleration by impingement upon a solidsurface.

As shown in FIG. 5, four distinct regions appear on the fiber length vs.free-fall distance curve. For free-fall distances less than the distanceD denoting the freeze point of the stream, the stream is yet molten andany attempt to collect the stream at lesser distances results in amolten mass. (The freeze point is taken in the pragmatic sense to denotethat point along a solidifying stream at which discrete particles havingan aspect ratio greater than unity are obtained upon intercepting thestream at that point; thus, interception at any upstream point by achosen mode of deceleration results, by this pragmatic definition, in anindiscrete, as opposed to particalized, mass. For distances intermediatethe points D and D fiber length is seen to increase in an exponentialfashion with increasing free-fall distance. Although the stream is atleast partially solid in this region, a disturbance sufficient todisrupt it is caused by the chosen deceleration, such as impingementupon a deflector plate or the like. At free-fall distances intermediatepoints D and D indefinite lengths may be collected. When the stream isallowed to fall unhindered through distances greater than D the tensileforce due to increasing stream length (and, therefore, weight) issufficient to cause stream breakage. Thus, at points below D relativelyuniform fiber lengths independent of free-fall distance may be obtained.

As will be illustrated, the relative and absolute positions of thepoints D D and D may be manipulated as desired by suitable variations ofthe process parameters. For example, the points D and D may occupyrelative positions such that D occurs upstream of D in such case, thereis no free-fall distance at which continuous length filaments can becollected. Such a circumstance may arise by numerous combinations offactors affecting the force system imposed upon the stream, but it isfound to be a particular problem in the case of spinning high densitymelts, especially in the larger diameter range. In such cases, the forcesystem acting upon the stream must, if indefinite length production isto be obtained be modified in light of the present teachings such thatthe tensile break point D is caused to be shifted downstream relative tothe point D and the demarcation between Zones A and B maintained at aposition intermediate the deceleration break points D and D Thus, theupstream portion denoted by Zone A must extend downstream of D and thedownstream portion denoted by Zone B must extend upstream of D with theresult that a stabilized stream deviation is formed between the points Dand D to thereby effect a smooth deceleration of the stream withoutbreakage.

An effective aid in determining stream continuity relative to free-falldistance may take the form of a simple electrical continuity circuittester, such as schematically diagramed in FIG. 6. As there indicated,such a tester serves to electrically interconnect the collection surfacewith the melt crucible to thereby sense electrical continuity, or lackof it, between the collection surface and the spinning head throughwhich an electrically conducting melt is being issued. Similardeterminations are, of course, made by directly measuring the fiberlengths obtained at varying free-fall distances, but use of thecontinuity tester allows one to monitor stream continuity continuouslyand to modify spinning conditions accordingly.

As previously indicated, the fiber lengths obtained under variousprocess conditions will vary in a characteristic manner with free-falldistance, as shown in FIG. 5. Indications of the mechanism by whichstream breakup occurs in the regions above the impact breakagedeceleration point D and below the point of tensile breakagedeceleration D are obtained by relating fiber length to free-falldistance to indicate where and when stream breakage occurred, whileexamination of the ends of broken lengths serve to indicate stream stateat the position of break as well as the rapidity of the break. In thelower portion of FIG. 5 is shown a recording of the continuity testerfor the typical graph appearing thereabove. In relating this recordingto the free-fall distance curve, it may be observed that the freezepoint D of the stream is the point below which fibrous shapes, asopposed to a molten mass, may be collected. Thus, when the stream isimpinged upon an electrically conductive surface at distances less thanD there is electrical continuity between the collection surface and thespinning head via the liquid stream, as indicated by the continuouspositive deflection on the recorder curve. For free-fall distancesbetween D and D,, the on-olf shape of the continuity curve indicatesthat the impingement 0f the stream upon the collection surface initiatesa disturbance suflicient to effect stream breakage at some pointupstream of the collection surface. An examination of the fiber endsobtained by collection within this region indicates that stream breakageoccurs very rapidly, but after solidification sufficient to retain afibrous shape. Thus, the disturbances set up in the stream uponimpingement on the collection surface at these free-fall distances aresufiicient to physically disrupt the stream and only broken lengths canbe obtained.

As indicated by the graph of FIG. 5, continuous fibers are obtained forfree-fall distances between points D and D the continuity tester ofcourse indicates electrical continuity within this region.

For distances greater than D the stream undergoes breakage beforeimpingement upon the collection surface. Because the stream acceleratingforce, normally due to gravity, has beyond this point become greaterthan the sum of stream strength and any upstream-acting drag forcegenerated under the chosen spinning conditions, the stream is caused tobreak prior to contacting the collection surface. Thus, the recordingindicates a continuously open circuit. The appearance of the ends on thebroken lengths obtained at free-fall distances greater than D, indicatethat they break in a very hot, solid region or in the liquid region;further, the lengths of the resultant fibers indicate that they breakvery near the freeze point.

As related in greater detail in the previously referenced copendin-gapplication Ser. No. 863,311 the position of the point D and D may beshifted relative to the orifice and to one another. Any one or more of anumber of spinning parameters are readily manipulated to attain thedesired relationship. Among the more significant parameters, there maybe mentioned those of reactant and coolant gas composition concentrationand velocity in those cases where the liquid region of the stream isbeing stabilized by the formation of a film as it issues; also, thespinning or stream velocity and the spinning temperature may as well bevaried to achieve similar results. For example, where the liquid regionof the stream is film stabilized by a reaction between the stream andthe spin gas, an increase in the reactant gas concentration may resultin a stabilizing film of increased thickness and, consequently,strength, resulting in both an upstream shift of the impact break pointD,,, as well as a downstream shift of the tensile break point DSimilarly, film thickness and strength may be increased by an increasein the spinning temperature to result in a more rapid rate of filmformation; however, any gain in total stream strength may becompromised, if not more than offset, by the postponement of streamsolidification due to the increased spinning temperature. A further modeof varying the spatial interrelationship of the points D and D isaccomplished by varying the spinning or extrusion velocity (V Forexample, with all other conditions fixed, an increase in spinningvelocity is accompanied by an increase in both viscous drag and the rateof heat transfer to the spin gas; thus, by virtue of the buoying effectof increased drag, the tensile break point D is caused to shiftdownstream, while the increase in heat transfer is offset by theincreased spinning velocity to normally result in a relatively verysmall down stream shift of the imp-act breakage point D, to therebyenlarge the region within which indefinite lengths may be collected.

The foregoing are but limited illustrations of the great variety ofmanipulations which are readily accomplished to attain the desiredarrangement of the points D and D In all cases, the essentialarrangement for continuous length production is one characterized by thepoint D occupying a position upstream of the point D with thedemarcation between the diiferential force systems of Zones A and Bbeing established therebetween.

In exemplifying the practice of the present invention, the simplifiedspinning assembly schematically depicted in FIG. 4 was employed. In thecase of the lead/ tin runs set out in Example I the assembly comprises astainless steel melt crucible enclosed by an upper header plate 12 and alower orifice plate 14, each of which are in sealing engagement withcrucible 10 to define a gas-tight melt chamber 16. Seated centrally oforifice plate 14 is a watchsized jewel 18 formed of a materialchemically compatible with the melt to be processed and drilled toprovide a suitable spinning orifice 20. In the case of Example I a rubyjewel having an orifice diameter of 100 microns and a length/diameterratio of unit was employed. Melting of the spin charge within chamber 16was accomplished by means of electrical resistance heating elements 22and charge temperature was monitored by thermocouple probe 24.Preferably, the spinning charge is melted under a vac,

uum just prior to effecting extrusion under an inert gas pressure, suchas argon. This may readily be accomplished by the two-way valvearrangement indicated at 26, whereby chamber 16 may be alternatelyevacuated and pressurized to eifect the desired rate of extrusion. Inorder to localize the various reactant and cooling gas mixturesemployed, a Pyrex spin gas column 28 is arranged concent-rically ofstream 29 issuing from orifice 20. The spin gas mixture is suppliedthrough conduit 30 to be gently deployed over the spin gas column crosssection by means of a gas distribution ring 32 provided with equi-spacedgas orifices 34; preferably, the orifices are oriented to discharge at aslightly downstream angle to assure effective spin gas circulation. Thespin gas column 28 defining Zone A has an inside diameter of 6 inchesand a length measured from orifice plate 14 of approximately 3 feet.Disposed immediately downstream of the spin gas column is the supportgas column 36 provided with a pair of extending conduits 38 and 40through which the support gas is introduced and extracted in a manner toeffect the desired circulation, whether co-current, counter-current, orvirtually stagnant. The direction and magnitude of the support gasvelocity is of course determined according to the amount of viscous dragit is desired to impose upon the stream within Zone B. In the exampleshere reported, the spin gas column 36 had an inside diameter of 4 inchesand length of approximately 4 feet and was of Pyrex construction. Thelower extremity of spin gas column 36 tapers to a central outlet 42through which the now solidified stream is withdrawn and taken up. Thereactant/ coolant gas mixture is normally introduced in the upper regionof spin gas column 28 in a fashion such that the flow is a gentlesweeping one although, depending primarily upon melt density, streamdiameter and spinning velocity, it may be found desirable to introducethe spin gas with a pronounced upstream or downstream velocity.Optionally, there may be provided a deflection plate 44 located at thedemarcation between Zones A and B to invoke the desired initialdeflection of the stream as it enters Zone B. In many operations,however, it will be found desirable to establish a suflicientdifferential in the force systems between Zones A and B such that thestream is readily contorted to the helical configuration when passinginto Zone B without the aid of a deflection plate. As previouslyexplained, this is accomplished by maintaining a drag force within ZoneB sufiicient to establish an angle of threshold deviation 0 small enoughto be exceeded by incidental stream deviations.

As depicted in FIG. 4, the stream 29, on entering the higher drag Zone Bbecomes aerodynamically contorted to a substantially helicalconfiguration to thereby define a drag-sustained accumulation withinZone B out of which the stream may be withdrawn without disruption. Asbefore related, where it is desired to extract indefinite lengths, thedemarcation between Zones A and B must be maintained at a pointintermediate the points of impact and tensile breakage deceleration, itis to be emphasized that the above-described spinning assembly merelyrepresents a simplified implementation of the present invention, thelatter being in no way limited to the details of the apparatus. Thelength of the spin gas and support gas columns 28 and 36, respectively,defining Zones A and B may, by suitable variation of the processparameters as hereinbefore discussed, vary over wide ranges. Also, thedepiction in FIG. 4 of a support gas column 36 of reduced diameterrelative to the spin gas column 28 is but one technique for controllingviscous drag through a control of spin and support gas velocities. ItWill often be just as feasible to employ one continuous column length,the Zone B or lower region of which would contain, for example, a densergas, or one moving at a lower co-current or higher counter-currentvelocity, as the case may be.

EXAMPLE I The spinning assembly previously described with reference toFIG. 4 was employed and the spinning charge was in the form of a mixtureof '62 weight percent lead/ 38 weight percent tin. The stream wasfilm-stabilized by extrusion into an oxygen-containing atmosphere toform an oxide stabilizing film upon the stream as it was given issue. Areactant/cooling gas mixture of 7 vol. percent oxygen/93 vol. percenthelium at room temperature was introduced through distribution ring 32as a gentle sweeping action at a flow rate of approximately 3.6 c.f.m.Atmospheric air was employed as the support gas within Zone B and wasintroduced as a counter-current flow of the magnitude set out in theaccompanying table. Extrusion was through a 100 micron diameter orificeformed in a watch-sized ruby jewel, the orifice having an L/D ratio ofunity to form a stream diameter of 85 microns. Preferably, heating tomelt was accomplished under a vacuum of below 100 microns of mercurypressure and extrusion was commenced prior to introducing the spin gasinto the spinning column. The gas distribution ring 32 was positionedapproximately 30 cm. below the orifice. The helium flow rate, whichfunctions as a coolant gas, was maintained constant at 3.3 c.f.m. tomaintain a relatively constant heat transfer rate, the oxygen flow ratebeing varied to obtain the desired volume percent oxygen in the mixture.

The runs set out in the table below were made under the conditionsspecified wherein there was determined, for increasing extrusion orstream velocities, the minimum support gas velocity within Zone Bnecessary to sustain a helical deviation stabilized about thedemarcation between Zones A and B.

SUPPORT GSAS VELOCITY FOR HELIX STABILIZATION Pb/Sn SUPPORTED BY AIRExtrusion at- Support gas Extrusion Velocity Detlecvelocity temperaturePressure Rate (c1u./ tion (cm./ C.) (p.s.i.g.) (g./miu.) sec.) platesec.)

9. 9 330 YcS 335 10 9.9 330 No -330 20 17. l 570 -270 20 17. l 570 -3l540 23.8 790 254 40 23. 8 790 320 G0 34. 6 l, 150 200 G0 34. 6 1,150 250so 42. 2 1, 400 -110 80 42. 2 1,400 -180 1 The positive direction isdownward or cocurrent with the stream. Notice that for theseexperimental conditions, the minimum countercurrent support gas velocityto maintain a helical configuration in Zone 13, varies only slightlywith the extrusion, or fiber, velocity. This is because of the changingmomentum of the extruded stream and follows closely the theoreticalrequirements predicted by Equation 2. Notice also that the provision ofa deflection plate intermediate Zones A and B slightly decreases thenecessary relative gas/fiber velocities to maintain the liber helicalconfiguration as predicted by theory.

EXAMPLE II The spinning assembly of Example I was employed with thefollowing modifications: The crucible was entirely constructed ofmolybdenum, the orifice being formed in a molybdenum insert seated inthe floor of the crucible and having a diameter of 4 mils and a lengthof 2 mils, to give an L/D ratio of 0.5; the support column 36 of FIG. 4was removed, the stream being supported in stagnant room air on exitingthe spin gas column 28; the crucible was inductively heated.

The melt composition was in the form of a 50 wt. percent aluminumoxide/50 wt. percent calcium oxide. In proceeding to spin, the melt washeated from room temperature to approximately 1,000 C. under a highvacuum of less than 10 microns; further heating from 1,000 C. throughthe melting point of approximately 1360 C. to a spinning temperature ofapproximately 1650 C. was under one atmosphere of argon; extrusionpressure was varied within the range of 30 to 100 p.s.i.g. Propane wasemployed as the film stabilization gas and introduced at a rate of 4c.f.h. to form a carbon film upon the stream through pyrolysis of thepropane, and; the cooling gas was helium supplied at a rate of 70 c.f.h.Again, the support gas was in the form of stagnant room air existingimmediately below the spin gas column 28, to thereby define Zone B.

Proceeding under these conditions, it was found that when the spinningor stream velocity (V was maintained within the range of from 600 to 680cm./sec., the stream was observed to remain quite straight in passingthrough the helium/propane atmosphere within the spin gas column 28.When the stream emerged from the helium/propane mixture into stagnantroom air at approximately 3 ft. from the orifice, the resultant increasein viscous drag force caused the stream to assume a helicalconfiguration, the upper extremity of which was stabilized about thelower extremity of the spin gas column. As before explained, this resultwas due to the fact that the drag force below the spin gas column was ofsuch magnitude as to sustain a rate of helical propagation greater thanthe stream velocity, whereas the viscous drag within the spin gas columnwas inadequate to sustain a propagation rate exceeding stream velocity.

Upon further increasing stream velocity to a value greater than 680cm./sec., the stream was observed to be deflected into a helicalconfiguration with the helium/ propane atmosphere of the spin gascolumn. Only by the utilization of a co-current spin gas velocitysulficient to maintain the relative velocity between the stream and thespin gas at a value less than 680 cm./ sec. within Zone A, would theresultant stream remain undeviated due to viscous drag and fall in astraight path until exiting the spin gas column to thereat assume thehelical configuration.

The foregoing has disclosed an improved stabilization process by whichfilament take-up can be practiced as the filament forms. In a firstregion the drag-sustained deviations are prevented from moving up intothe fragile liquid portion of the stream while simultaneously the draginteraction is utilized to form a helical-like configuration in a secondregion beneath the first region Thus, a tension necessary for sometake-up techniques can be applied to the stream in the second regionwithout affecting the liquid portion of the stream.

While only certain specific embodiments and features of the presentinvention have been described, it will be understood by those skilled inthe art, that various changes and modifications may be made withoutdeparting from the invention as set forth. Accordingly, all suchmodifications and changes as fall within the true spirit and scope ofthe present invention are intended to be covered by the appended claims.

We claim:

1. In a process for forming filaments from a normally solid inorganicmelt having a viscosity not greater than 10 poises including the stepsof (a) extruding a free molten stream from the melt,

(b) exposing the extruded stream to a gaseous atmosphere to form a filmabout the periphery of the stream which film has sufficient strength tostabilize the stream against surface tension-induced breakup pendingsolidification,

the improvement which comprises passing the stream into a first gaseouszone which extends downstream below the point at which the streambecomes solidified so as to cause the velocity of the stream deviationsresulting from the drag interaction between the solidified stream andsaid first zone gas to be less than the stream velocity in said firstzone, and passing the stream into a second gaseous zone immediatelybelow said first zone so as to cause the velocity of the streamdeviations resulting from the drag interaction between the stream andsaid second zone gas to be greater than the stream velocity in saidsecond zone thereby resulting in the stream in said second zoneattaining a helicallike configuration and whereby tension, may beapplied thereto without transferral of the tension to the molten portionof said stream.

2. The process of claim 1 wherein the boundary between the first gaseouszone and the second gaseous zone lies intermediate a first point (D,,)upstream of which stream deceleration causes disruptions in the streamcontinuity and a second point (D downstream of which the net tensionalforce acting upon the stream causes 17 disruptions in the streamcontinuit, D being upstream of D 3. The process of claim 2 wherein theviscosity of the gas in the second gaseous zone is greater than theviscosity of the gas in the first gaseous zone.

4. The process of claim 2 wherein the density of the gas in the secondgaseous zone is greater than the density of the gas in the first gaseouszone.

5. The process of claim 2 wherein the gas in the second gaseous zone hasa counter-current flow.

6. The process of claim 2 wherein the gas in the first gaseous zone hasa co-current flow and the velocity of the gas in the second gaseous zoneis less than the velocity of the gas in the first gaseous zone.

7. The process of claim 2 wherein the stream is a metal or alloythereof.

References Cited UNITED STATES PATENTS 2,825,108 3/1958 Pond 22 200.12,879,566 3/1959 Pond 22-200.1 2,900,708 8/1959 Pond 29 194 2,907,08210/1959 Pond 22 57.2 2,940,886 6/1960 Nachtman 154 91 2,976,590 3/1961Pond 22 200.1 3,214,805 11/1965 McKenica 22-2001 3,216,076 11/1965 Alberet a1 22-200.1

18 3,218,681 11/1965 Ditto 22-57.2 3,429,722 2/1969 Economy et a1.106-55 3,461,943 8/1969 Schile 16489 3,481,390 12/1969 Velfvi et a1164-86 3,490,516 1/1970 Basche et a1 164273 3,516,478 6/1970 Dunn et a1.164-281 3,543,831 12/1970 Schile 164-82 3,583,027 6/1971 Garrett et a1188 3,593,775 7/1971 Privott et al. 164 -82 3,602,291 8/1971 Pond 164-823,613,158 10/1971 Mottern et a1. 264176 Z 3,614,808 10/1971 Harrison etal 264176 Z FOREIGN PATENTS 1,069,472 5/1967 Great Britain 264176 ZOTHER REFERENCES The preparation of thin Wires by solidification ofliquid metals jets, by Tammann et a1.

Zeifschrift fur Metallkunde, 27( 5 111-115 (1935 (Translation 5 pages),264-176 F.

JAY H. WOO, Primary Examiner US. Cl. X.R. 10655, 39; 16482; 264-168, 176F, 40, 232

